TEMPERATURE-GRADIENT CHAMBERS FOR RESEARCH ON GLOBAL ENVIRONMENT CHANGE .2. A TWIN-WALL TUNNEL SYSTEM FOR LOW-STATURE, FIELD-GROWN CROPS USING A SPLIT HEAT-PUMP

A temperature gradient chamber (TGC) is described which enables elevat ed CO2 concentrations and a dynamic temperature gradient to be imposed on field crops throughout their life cycle under standard husbandry. Air is circulated through two double-walled polyethylene-covered tunne ls connected to a split heat pump system to give a near-linear tempera ture gradient along each tunnel, Solar energy gain along each tunnel a nd exchange with outer tunnel air flow contribute to the temperature g radient and also produce diurnal and seasonal temperature fluctuations corresponding to ambient conditions, Mean temperature gradients of be tween 3 and 5 degrees C have been recorded throughout the growing seas ons of crops of lettuce, carrot, cauliflower and winter wheat, Elevate d or present CO2 concentrations are maintained in each of two pairs of tunnels throughout the cropping season using pure CO2 injected throug h motorized needle valves. This system can realistically simulate aspe cts of the effects of projected future environmental change on crop gr owth, development and yield, and in particular the possible interactio n of the effects of increased CO2 and temperature.